Digital radiographic volume imaging provides three-dimensional (3D) images that have been reconstructed from a series of 2D images taken over a succession of angles of the X-ray source relative to the detector. Acquisition of the 2D projection images used for cone beam CT can employ a large-area digital detector, such as a digital radiography (DR) detector that is typically used for conventional single projection radiography.
Computed tomography (CT) systems, such as cone beam computed tomography (CBCT) or cone beam CT systems offer considerable promise as one type of diagnostic tool for providing 3D volume images. Cone beam CT systems capture volume data sets using a high frame rate flat panel digital radiography (DR) detector and an X-ray source. The X-ray source and detector are typically affixed to a gantry that revolves about the object to be imaged, with the X-ray source directing, from various points along its orbit around the subject, a divergent cone beam of X-rays toward the subject. The CBCT system captures projection images throughout the source-detector orbit, for example, with one 2D projection image at every angular increment of rotation. The projections are then reconstructed into a 3D volume image using various techniques. Among the most common methods for reconstructing the 3D volume image are filtered back projection (FBP) approaches.
While there have been advantages for diagnosis afforded by 3D volume imaging, there are concerns related to repeated patient exposure to x-ray radiation. Various approaches have been proposed with the goal of limiting the number of exposures needed for accurate 3D volume reconstruction and maximizing the amount of information that can be obtained from a set of projection images. However, the number of exposures that are used for reconstruction affects image quality and can also have an impact on the number and severity of image artifacts in the reconstructed 3D volume image. One such artifact, generally termed view aliasing, can have a number of negative effects on the reconstructed volume, such as ripples, for example. View aliasing, well known to those skilled in the imaging arts, occurs when the signal frequency for captured image data exceeds a threshold Nyquist frequency.
Thus, it can be appreciated that there are advantages to image processing and volume reconstruction techniques that can reduce the number and severity of imaging artifacts while allowing imaging with a low level of patient exposure. It can also be appreciated that the processing directly impacts the time required before the volume image can be displayed and that this time can be reduced if intermediate computations can be used effectively.